1. Field of the Invention
The present invention relates to an apparatus for controlling an automatic transmission of a vehicle and, more particularly, to an apparatus for controlling an automatic transmission which selectively sets either of two gear shift modes, an automatic gear shift mode and a manual gear shift mode, and controls the automatic transmission according to the set gear shift mode.
2. Description of the Related Art
An apparatus for controlling an automatic transmission of a vehicle is disclosed in Japanese patent application laid-open No. 8-193656. The device has a gear change controller, which selectively sets either of two gear shift modes, an automatic gear shift mode and a manual gear shift mode. The device controls the automatic transmission according to the set gear shift mode and a constant speed travel controller controls the travel speed so as to be substantially constant when the travel mode of a vehicle is set in constant speed travel mode. With the gear shift mode being set in the manual gear shift mode and the travel mode being set in a constant speed travel mode, when the constant speed travel controller gives a gear change command, the conventional automatic gear change controller ignores the given gear change command and maintains the previously set gear shift stage.
Such a conventional automatic gear change controller, however, has a problem in maintaining a constant travel speed. That is, even though the travel load of a vehicle is changed, for example, when the road elevation changes from being level to an uphill, no control is carried out for changing the gear shift stage, causing difficulty in maintaining constant vehicle speed.
The present invention was developed in consideration of the aforementioned problems. An object of the present invention is to provide an automatic gear change controller which can maintain constant travel speed with the travel mode being set in a constant speed travel mode even though the gear shift mode is changed to the manual gear shift mode or the travel load of a vehicle changes.
An apparatus for controlling an automatic transmission according to the present invention comprises a transmission driving means for determining the gear shift stage of an automatic transmission which transmits rotational torque of an internal combustion engine to drive wheels of a vehicle in response to a gear change control signal; a gear change control means for selectively setting either of two gear shift modes, an automatic gear shift mode to determine the gear shift stage according to the travel speed, the amount of depression of the accelerator pedal and the throttle valve opening, and a manual gear shift mode to determine the gear shift stage corresponding to a shift position of the operating lever, and for determining the contents of said gear change control signal according to the set gear shift mode; a travel mode setting means for setting whether or not the travel state of the vehicle is to be a constant speed travel mode corresponding to manual operation; and a constant speed travel control means for giving a command signal for changing the gear shift stage to the gear change control means so as to make said travel speed substantially constant, and for giving a command signal for changing the valve opening to a throttle valve control means when said gear shift mode is set in the automatic gear shift mode and the travel mode is set in the constant speed travel mode, characterized in that, when the gear shift mode is set in manual gear shift mode and the travel mode is set in constant speed travel mode, the constant speed travel control means gives a downshift command signal and, when the accelerator pedal is depressed beyond a predetermined amount, the gear change control means shifts down the gear shift stage.
That is, according to the present invention, with the travel mode being set to the constant speed travel mode, torque can be transmitted to the wheels according to changes in the travel load of a vehicle even though the gear shift mode is changed to manual gear shift mode.